Rationale and Objectives
The aim of this study was to assess the repeatability and internal consistency of flow measurements in the renal arteries and pararenal aorta with the use of standard two-dimensional (2D) and novel four-dimensional (4D) phase contrast (PC) magnetic resonance imaging (MRI).
Materials and Methods
Ten healthy volunteers were imaged with a radially undersampled 4D PC technique centered over the renal arteries and with four 2D PC slices placed in the supra/infrarenal aorta and the left/right renal arteries; this MRI exam was performed twice on each subject. Flow measurements in all four vessels were computed from 2D and 4D PC data sets. Student’s t -tests ( P < .05) were used to assess differences between in-flow (suprarenal aorta) and out-flow (infrarenal aorta + left renal artery + right renal artery) for the 2D and 4D techniques, to compare in- and out-flow, and to compare repeated measurements of 2D and 4D flow measurements.
Results
No significant differences were found in repeated measurements of 2D ( P = .15) or 4D ( P = .39) data. No significant difference was found between 2D (3.4 ± 2.8 mL/cardiac cycle) and 4D (3.5 ± 2.7 mL/cardiac cycle) in- and out-flow differences ( P = .88). Out-flow was greater than in-flow for 2D measurements ( P = .003); no difference was found for 4D measurements.
Conclusion
The 2D and 4D techniques demonstrated strong repeatability and internal consistency of flow measurements in the renal arteries and pararenal aorta.
In recent years, four-dimensional (4D) phase contrast (PC) magnetic resonance imaging (MRI) has become more common as a research tool to investigate anatomy, angiography, and flow and velocity information. 4D PC acquisitions provide large volumetric coverage and three-directional velocity encoding for multiple time points in the cardiac cycle. Additionally, 4D PC data sets can be used to derive various flow-related parameters, including pulse wave velocity, pressure gradients, and wall shear stress . A number of studies have been performed to validate 4D PC flow measurements, such as the comparison of 4D PC flow measurements to flow phantoms and to two-dimensional (2D) flow measurements as a reference standard . 4D PC flow measurements have also been compared with laser Doppler velocimetry and with ultrasound flow measurements in the cranial vessels and the left ventricle . Furthermore, pressure gradients derived from 4D PC data sets have been validated with invasive pressure probes . Initial studies showed that pressure gradients measured with 4D PC and invasive pressure probes were found to be in strong agreement in the carotid and iliac arteries. Such studies are useful for demonstrating the feasibility of using 4D PC flow techniques clinically.
Navigator-based respiratory gating, as well as continuously adapting respiratory gating with bellows, has allowed for 4D PC data sets to be collected during free breathing . However, respiratory gating further prolongs the already lengthy acquisitions. Furthermore, the high demands for spatial resolution and large volume coverage needed to assess the complicated anatomy of the abdominal vasculature ( Fig 1 ) have hampered the use of 4D PC MRI in the abdomen. Radial undersampling has been promising as a means to overcome these limitations; radial undersampling has allowed for the assessment of renal flow in addition to the acquisition of high-quality PC angiograms without the need for an external contrast agent . Given the potential for artifacts arising from respiratory and peristaltic motion in abdominal exams, further evaluation is needed to assess the performance of 4D PC techniques in the abdomen.
Open full size image
Figure 1
Vascular geometry and hemodynamics in the abdominal aorta and renal arteries of a healthy volunteer. Three-dimensional stream lines depict the systolic blood flow in the abdominal vasculature. Planes demonstrate velocities in the suprarenal aorta (SRA), infrarenal aorta (IRA), and left/right renal arteries (LRA/RRA).
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Materials and methods
Subjects
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MRI
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Data Analysis
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Statistical Analysis
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Results
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![Figure 3, Box and scatter plots of in-flow (suprarenal aorta [SRA]) and out-flow (infrarenal aorta [IRA] + left renal artery [LRA] + right renal artery [RRA]) in 10 volunteers as measured with two-dimensional (2D) and four-dimensional (4D) phase contrast (PC) techniques. Data shown are from both first and second exams in each subject.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/RepeatabilityandInternalConsistencyofAbdominal2Dand4DPhaseContrastMRFlowMeasurements/1_1s20S1076633213000731.jpg)
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Discussion
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Acknowledgment
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